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Homework Help: Electric field please help

  1. Jan 12, 2008 #1
    Electric field....please help!!!!

    1. The problem statement, all variables and given/known data
    A 0.75 g plastic bead is charged by the addition of 8.28×10^10 excess electrons. What electric field (strength) will cause the bead to hang suspended in the air?


    2. Relevant equations



    3. The attempt at a solution
    Doesn't E have to equal the weight? So would I just calculate the weight of the bead? That seems to easy though...
     
  2. jcsd
  3. Jan 12, 2008 #2

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    The weight and the charge. Also, remember Force = E*q.
     
  4. Jan 12, 2008 #3
    So...
    (K*Q1*Q2) / R^2 = (KQ1) / R^2 * Q
    And then I solve for Q?
    But then I get Q2 = Q?? I am confused...
     
  5. Jan 12, 2008 #4

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    Let E be the unknown electric field. Then what is the force it exerts on a charge q? I've already told you...
     
  6. Jan 12, 2008 #5
    E = Force / Q
    Force = K*Q1*Q2 / r^2
     
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